Multilayer polymeric optical films are widely used for various purposes, including as mirrors and polarizers. These films often have extremely high reflectivity, while being lightweight and resistant to breakage. Examples of a wide variety of multilayer films are included in the commonly assigned U.S. Pat. No. 5,882,774, entitled “Optical Film,” which is hereby incorporated by reference. Exemplary applications include compact electronic displays, including liquid crystal displays (LCDs) placed in mobile telephones, personal data assistants, computers, televisions and other devices.
Known multilayer optical films have alternating layers of materials having differing indices of refraction. Polymethyl Methacrylate (PMMA) has been considered as the lower-index material in such films. PMMA is typically extruded at a temperature between 235 degrees C. and 250 degrees C. Thus, it is not ideally coextruded with high-index materials such as polyethylene terephthalate (PET), which is typically extruded at a minimum temperature of about 265 degrees C., or polyethylene naphthalate (PEN), which is typically extruded at a minimum temperature of about 270 degrees C.
Thus, there remains a need for a low-refractive-index material that is process compatible with high-refractive index polymers such as PET and PEN.